1. Field of the Invention
The present invention relates to a multipoint autofocus system which is capable of focusing on any object in a plurality of focus detection zones and a camera having such a multipoint autofocus system.
2. Description of the Related Art
In a single-lens reflex camera, it is common for a multipoint autofocus system, which is capable of focusing on a plurality of focus detection zones, to be provided. In a known pupil-division phase difference multipoint autofocus system provided in a single-lens reflex camera, a pair of object images obtained by pupil division are projected onto a line sensor array so that the defocus amount can be obtained based on a phase difference between the pair of object images formed on the line sensor array.
In recent years, a multipoint autofocus system having a cross sensor in which the defocus amount of object images in the same focus detection zone is detected by lateral line sensor arrays and longitudinal line sensor arrays has been proposed. For example, see Japanese Unexamined Patent Publication No. 2002-323650.
In an automatic selection of focus detection zones in a multipoint autofocus system, in many cases, a closest object is preferentially selected. If the focus detection is carried out by the cross sensor consisting of lateral and longitudinal line sensor arrays, either the lateral line sensor arrays or the longitudinal line sensor arrays may be theoretically focused because the focus detection is carried out for the same object.
However, if the object in one of the lateral and longitudinal line sensor arrays has a low contrast or contrast gradation, there is a possibility of failure to correctly detect a phase difference. If the phase difference is deviated on the short object distance side, the focusing lens is moved in the direction of the short object distance, thus resulting in AF hunting.